**3.1.3 Conclusions**

Daily ethanol

production

 (g L-1

d-1)

The utilization of whey UF permeate to ethanol in continuous fermentation is possible. *Kluyveromyces marxianus* was able to metabolize lactose and the total fermentation efficiency was as high as 95%. The lactose utilization and ethanol production were connected with the HRT. The maximum daily ethanol production of 8.61 g L-1d-1 was achieved when the HRT was 24 h and the ethanol yield was 0.203 g g-1. The results indicated that the HRT should be 24 h to obtain high rates of ethanol formation and to avoid product inhibition. Doubling the HRT to 48 h did not contribute to a noticeable increase of ethanol production and the daily ethanol production decreased to 7.73 g L-1d-1 while the ethanol yield was 0.325 g g-1.
